1. Field of the Invention
The present invention relates to a centrifugal pump of the vortex-flow type, and more particularly, but not exclusively, to a vortex-flow type pump or a vane type regenerative pump which includes a pump housing defining therein an arcuate pump chamber, and a disc-like impeller rotatably and axially movably assembled within the pump housing to be driven by a drive shaft and having opposite end faces each forming a close clearance with a corresponding internal end wall of the pump housing.
2. Description of the Prior Art
In FIG. 14 there is illustrated such a vortex-flow type single-stage pump as described above, wherein a disc-like impeller I has on either end face of the rim portion thereof a plurality of circumferentially spaced vane grooves V which cooperate with an arcuate pump chamber R.sub.1 in a pump housing H to discharge hydraulic fluid under high pressure from a discharge port of the pump chamber. The hydraulic fluid under high pressure tends to radially leak out of the discharge port into a central sealed chamber R.sub.2 through close clearances between opposite end faces of the impeller I and corresponding internal end walls of the pump housing and to further leak out of the sealed chamber R.sub.2 into a suction port of the pump chamber through the close clearances. Rotation of the impeller causes the hydraulic fluid in the close clearances to radially and circumferentially flow at an approximately half circumferential speed of the impeller. The difference in pressure between chambers R.sub.1 and R.sub.2 caused by the flow of hydraulic fluid at the circumferential speed is extremely small in comparison with the difference in pressure between suction and discharge ports of the pump chamber R.sub.1. As a result, the pressure in sealed chamber R.sub.2 becomes an approximately intermediate value between the suction and discharge pressures.
In the case that the impeller is in the form of such a conical disc-like impeller as exaggeratedly illustrated in FIG. 15, the pressures acting on opposite end faces of the impeller respectively at A and B parts of the pump chamber in FIG. 16 occur as illustrated in a graph of FIG. 17 where a solid line represents the pressure distribution on the upper end face of the impeller, and broken lines represent the pressure distribution on the bottom end face of the impeller. The pressure distribution is caused by the fact that although the impeller is applied at the opposite end faces thereof with the same pressure respectively in the chambers R.sub.1 and R.sub.2, the pressure in a smaller clearance between the bottom end face of the impeller and the corresponding internal end wall of the pump housing changes more greatly than the pressure in a larger clearance between the upper end face of the impeller and the corresponding internal end wall of the pump housing. As a result, the impeller is applied at the low pressure side thereof with an upward thrust force Fa and at the high pressure side thereof with a downward thrust force Fb. As illustrated in FIG. 18, therefore, the upper end faces of impeller I is brought into contact with the internal end wall of the pump housing at the low pressure side, while the bottom end face of impeller I is brought into contact with the internal end of the pump housing at the high pressure side. This results in a noticeable increase of radial pressure gradient at the contact portions with the internal end walls of the pump housing. Thus, the pressure distribution on the impeller I changes as illustrated in FIG. 19. For the foregoing reasons, the impeller I will be defaced by frictional engagement with the internal end walls of the pump housing during rotation thereof, resulting in loss of the power applied to the pump.
In the case that the vortex-flow type pump is in the form of a two stage pump as illustrated in FIG. 20, the pressure in a central sealed chamber R.sub.2 becomes approximately equal to the pressure in the discharge port of the first stage and to the pressure in the suction port of the second stage. Thus, the pressure distribution on the opposite end faces of the first stage impeller I is caused as illustrated in FIG. 22, and as illustrated in FIG. 21, the first stage impeller I is brought into contact with the internal end wall of the pump housing due to an upward thrust force applied thereto, resulting in defacement of the upper end face of the first stage impeller and loss of the power applied to the pump. Similarly, the pressure distribution on the opposite end faces of the second stage impeller is caused as illustrated in FIG. 24, and as illustrated in FIG. 23, the second stage impeller is brought into contact with the internal end wall of the pump casing due to a downward thrust force applied thereto, resulting in defacement of the bottom end face of the second stage impeller and loss of the power applied to the pump.
In the case that both the impellers in the two stage pump are each in the form of a flat disc-like impeller, as illustrated in FIG. 25, the second stage impeller is tilted by an upward thrust force applied thereto at the low pressure side thereof and a downward thrust force applied thereto at the high pressure side thereof. The pressure distribution on the opposite end faces of the second stage impeller is caused as illustrated in FIG. 26. This results in an increase of the thrust forces acting on the second stage impeller, causing defacement of the impeller and loss of the power applied to the pump.